During the shut-down process of a high-speed compressor, such as a centrifugal compressor, and after the compressor remains idle at zero speed, the pressure inside the compressor casing eventually reaches what is known as “settle-out” pressure. At settle-out pressure, the pressures inside the compressor and any process piping connected thereto reach an equilibrium that will typically remain until the system is either vented or restarted. Current seal technology implemented in high-pressure compressors is limited as to how high the settle-out pressure can reach before exceeding the current state of the art of internal seals, such as gas seals, and thereby risking potential seal failure.
One common method of circumventing this occurrence is to overdesign the machine and accompanying process system such that the projected settle-out pressure is always within the design range of the seal system. Oftentimes, this can involve designing and installing an expensive and inexperienced prototype seal. Unfortunately, prototype seals often have unknown reliability and are designed only for the application at hand. Another common method of reducing the effects of settle-out pressure is to design the process system to favor the suction (i.e., low pressure) volume of the compressor system, and minimizing the volume of the high pressure system isolated by the shut down valve. This frequently results, however, in larger and more costly process systems.
What is needed, therefore, is a system and method configured to allow a high-pressure compressor to settle-out at reduced pressure levels while simultaneously reducing blow-down seal leakage during normal operation.